The present application relates to a secondary battery that includes a gel electrolyte, to a battery pack, an electric vehicle, an electric power storage system, an electric power tool, and an electronic apparatus that use the secondary battery.
In recent years, various electronic apparatuses such as a mobile phone and a personal digital assistant (PDA) have been widely used, and it has been strongly demanded to further reduce the size and the weight of the electronic apparatuses and to achieve their long life. Accordingly, as an electric power source for the electronic apparatuses, a battery, in particular, a small and light-weight secondary battery capable of providing high energy density has been developed. In these days, it has been considered to apply such a secondary battery to various other applications represented by a battery pack attachably and detachably mounted on the electronic apparatuses or the like, an electric vehicle such as an electric automobile, an electric power storage system such as a home electric power server, or an electric power tool such as an electric drill.
As the secondary battery, secondary batteries that obtain a battery capacity by utilizing various charge and discharge principles have been proposed. Specially, a secondary battery utilizing insertion and extraction of an electrode reactant is considered promising, since such a secondary battery provides higher energy density than lead batteries, nickel cadmium batteries, and the like.
The secondary battery includes a cathode, an anode, and an electrolytic solution. The electrolytic solution contains a solvent and an electrolyte salt. The electrolytic solution functioning as a medium for a charge and discharge reaction largely affects performance of the secondary battery. Therefore, various studies have been made on the composition of the electrolytic solution. Specifically, to suppress battery degradation at the time of high-voltage charging, explosion hazard due to pressure increase inside a battery, and/or the like, a cyclic ester carbonate having one or more carbon-carbon unsaturated bonds is used as an additive of an electrolytic solution (for example, see Japanese Unexamined Patent Application Publication Nos. 2006-114388, 2001-135351, H11-191319, 2000-058122, and 2008-010414; and Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2004-523073). This kind of cyclic ester carbonate is used not only for a battery system using an electrolytic solution (liquid battery), but also for a battery system not using an electrolytic solution (solid battery) (for example, see Japanese Unexamined Patent Application Publication No. 2003-017121).